1. Field of the Invention
This invention relates to x-ray imaging technology, and more particularly relates to a monolithic x-ray image detector for use with digital signal image processing.
2. Background Information
Recently there has been great interest in improving diagnostic techniques from x-rays. These efforts include sophisticated image signal processing to improve detection and diagnosis of cancer in patients. In this process, an x-ray image is digitized for processing by computer software. This technology has been developed because the resolution achieved with the present x-ray techniques, is only in the range of 100 to 200 dots per inch (dpi), and is dependent upon exposure and the development process. With digital image signal processing, significant improvements in the early detection diagnosis of cancer has been achieved.
In one application described in Physics Today, June 1995, Pages 21 and 22, digital image signal processing has revealed potentially cancerous calcifications that would probably be missed with the usual x-ray techniques. For example, current mammogram techniques only show micro calcifications in the range of 250 microns or greater; smaller tell-tale micro calcifications would be missed or require additional diagnostic procedures to verify. Digital image signal processing combined with current film techniques to digitize a mammogram, has shown promise of detecting micro-calcifications in the range of 50 to 100 microns. Digitizing an image in this matter, to improve detection of a weak signal in a complex background, resulted from signal processing to detect a faint star in a blurry image. This clearly suggests that an enhanced image can greatly improve the results of current imaging techniques.
Present x-ray techniques are also limited by the film to create the images. Not only is the image resolution limited, but large object images are not generally possible. Large scale imaging or full torso x-rays in medical applications as well as large object imaging for industrial applications, is needed.
Another disadvantage of present x-ray techniques is that the application of x-ray depends upon the film sensitivity. Thus, the dosage of x-rays has to be sufficiently high to produce a good,useful image even with currently developed digital image signal processing. Further, digitization of an x-ray image is a difficult and time-consuming process. A higher resolution image than those presently available from x-ray film, that is directly available for digital image signal processing or image construction would be a great advantage.
It is thus, one object of the present invention, to provide an x-ray image detector that will provide higher resolution than x-ray film.
Another object of the present invention is to provide an x-ray image detector that has higher sensitivity than the usual x-ray film permitting a lower dosage of x-rays.
Yet another object of the present invention is to provide an x-ray image detector that includes integrated read-out electronics so that an image is directly available for digital image signal processing.
Still another object of the present invention is to provide a monolithic x-ray image detector that is rugged and can be built into x-ray devices used on-site with portable x-ray equipment.
Still another object of the present invention is to provide a monolithic x-ray image detector comprised of P-type/intrinsic/N-type (PIN) diodes and read-out electronics produced on a high resistance silicon substrate which incorporates dielectric isolation providing three-dimensional integration.
Yet another object of the present invention is to provide x-ray imaging sensors that are constructed from detector elements that allow the die to be very closely abutted to provide edge-to-edge detection capabilities.
Still another object of the present invention is to provide an x-ray image detector having integrated read-out electronics and PIN diodes that permit die to be formed into panels for use in large object imaging.